RO membranes for low salinity water

The new membranes – models LS-HO-8540 and LS-HO-8040 – will provide more compact, lower-cost RO systems for a range of low salinity applications, the company claims. These include desalination of brackish well water, treatment of low salinity surface water and treatment/reuse of wastewater. The new products incorporate an aramid, hollow fibre membrane and use DuPont’s patented HF Cartridge technology.

DuPont claims that the new HF Cartridges have a higher output than any other membrane in terms of GPD of product water per unit volume of membrane. The LS-HO-8540 membrane has a nearly 30% higher output than a similar HF Cartridge product designed primarily for brackish water desalination. The output is reckoned to be more than twice that of a typical, spiral-wound RO element. The higher output enables compact and efficient RO systems to be designed and built with:

• about half the number of HF Cartridges compared to spiral membranes;
• system savings due to fewer RO stages, less supporting equipment and less pipework and fittings;
• space savings due to higher capacity per unit volume;
• and less membrane handling.

The benefits of higher output and compactness become most attractive in lower salinity applications ranging from mildly brackish feed water down to a salinity of less than 100mg/l TDS (due to the lower pressure drop of the HF Cartridge membrane, compared to the spiral element).

The low membrane flux, combined with the design of the HF Cartridge, can provide advantages not offered by spiral-wound elements, especially in high fouling surface water and wastewater treatment/reuse applications.

The low flux of about 3GPD per square foot of membrane surface – at 225 psi (15 bar) operating pressure – is less prone to fouling than the higher fluxes used with spiral elements (typically three to five times higher) in designing RO systems. One of the key objectives in developing the HF Cartridge technology for low salinity applications was to reduce membrane fouling by coupling the improved internal flow hydraulics of the new device with the low membrane flux.

An important related tool for controlling membrane performance and operating cost in RO systems, designed for high fouling applications, is advanced membrane cleaning technology. Use of proprietary cleaning technology for cleaning HF Cartridge membranes is less expensive than buying new membranes for replacement of old.

Applications of the new, low salinity, high output cartridges are expected to range from potable water production, to light industrial and commercial water treatment, to wastewater treatment. The LS-HO-8540 model is intended for new RO systems. The LS-HO-8040 is intended to replace typical 8 inch (20mm) diameter spiral-wound elements in existing systems, where more RO system capacity is needed.

The new products are expected to find use in a range of RO system sizes. In small standard systems, typically ranging from 5000 to 100,000GPD, OEM’s can benefit from the compactness and high conversion capability of the HF Cartridge. In large multi-million-GPD plants, the same efficiencies can be achieved, coupled with more significant savings in costs of civil works.